Transdermal drug delivery (TDD) offers several advantages over traditional delivery methods including injections and oral delivery. When compared to oral delivery, TDD avoids gastrointestinal drug metabolism, reduces first-pass effects, and provides sustained release of drugs for up to seven days. When compared to injections, TDD eliminates the associated pain and the possibility of infection. Theoretically, the transdermal route of drug administration could be advantageous in the delivery of many therapeutic proteins because proteins are susceptible to gastrointestinal degradation and exhibit poor gastrointestinal uptake. Proteins such as interferon are cleared rapidly from the blood and need to be delivered at a sustained rate in order to maintain their blood concentration at a high value, and transdermal devices are easier to use than injections (U.S. Pat. No. 5,814,599).
In spite of these advantages, very few drugs and no proteins or peptides are currently administered transdermally for clinical applications because of the low skin permeability to drugs. This low permeability is attributed to the stratum corneum (SC), the outermost skin layer which consists of flat, dead cells filled with keratin fibers (keratinocytes) surrounded by lipid bilayer. The highly-ordered structure of the lipid bilayer confers an impermeable character to the SC (U.S. Pat. No. 5,814,599).
Transdermal drug delivery offers an advantageous alternative to oral delivery and injections. However, its applications are restricted to only a few drugs because of the extremely low skin permeability to drugs. Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies, especially in connection with an improved method for transdermal drug delivery.